Methods for Treating Filled Microporous Membranes

ABSTRACT

The present invention is directed to a method for treating a surface of a filled microporous membrane. The microporous membrane includes a polyolefinic matrix, inorganic filler distributed throughout the matrix, and a network of interconnecting pores throughout the membrane. The method includes sequentially (1) contacting the membrane with a first treatment composition comprising an epoxy-silane which is in intimate contact with the inorganic filler; (2) subjecting the membrane of (1) to conditions sufficient to effect a first reaction between the inorganic filler and the silane groups of the epoxy-silane compound; (3) contacting the membrane of (2) with a second treatment composition comprising polyalkylene polyamine, an amine functional polysaccharide and/or an amino silane; and (4) subjecting the membrane of (3) to conditions sufficient to effect a second reaction. Treated membranes also are provided.

FIELD OF THE INVENTION

The present invention relates to methods for treating microporousmembranes useful as filtration and adsorption media, and to microporousmembranes prepared by the methods.

BACKGROUND OF THE INVENTION

According to the Department of Energy, 21 billion gallons of co-producedwater are drawn up by oil and gas wells each year in the United States.Natural “oil” from a well is actually a multiphase fluid ofoil/water/gas. Generally, all three fluids are found in everyhydrocarbon well and well effluent.

Because of its value and because of environmental concerns, oil needs tobe separated from this effluent. This is usually done throughgravitational settling in large tanks, which requires capital andsignificant space that is not always available onsite. Gas is separatedeasily in a mechanical separator or by pressure reduction within storagecontainers. In the case of heavy oils and many emulsified fluid systems,the raw fluids are heated to change the density of the oil and water byheating off lighter ends and essentially agitating their molecularstructures so that these fluids can more easily separate. Water then isa byproduct.

Filled microporous membranes are known to be low cost, efficient andenvironmentally friendly separation media for the separation of oil frombyproduct water as mentioned above. Notwithstanding, as with mostfiltration media, over a period of time the filtration membranes canbecome fouled with residual oil and other contaminants. Such fouling candecrease the flux rates and, thus, reduce the efficiency of the filterdevices. Hence, it would be desirable to provide a microporous membranefor use as an extended life filtration medium having improvedanti-fouling properties while maintaining a high flux rate. The methodsfor treating filled microporous membranes as disclosed and claimedherein provide such improved anti-fouling properties.

SUMMARY OF THE INVENTION

The present invention is directed to a method for treating a surface ofa filled microporous membrane. The microporous membrane comprises apolyolefinic polymeric matrix, finely divided, particulate,substantially water-insoluble inorganic filler distributed throughoutthe matrix, and a network of interconnecting pores communicatingthroughout the microporous membrane. The method comprises sequentially(1) contacting the membrane with a first treatment compositioncomprising an epoxy-silane compound having at least one epoxy group andat least one silane group, wherein the epoxy-silane compound is inintimate contact with the inorganic filler present in the matrix; (2)subjecting the membrane of (1) to conditions sufficient to effect afirst reaction between the inorganic filler and the silane groups of theepoxy-silane compound, wherein the first reaction effected is at least acondensation reaction; (3) contacting the membrane of (2) with a secondtreatment composition comprising polyalkylene polyamine, an aminefunctional polysaccharide and/or an amino silane; and (4) subjecting themembrane of (3) to conditions sufficient to effect a second reaction,wherein the second reaction effected is at least an epoxy ring-openingreaction.

The present invention also is directed to treated microporous membranesprepared by the various claimed methods.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a plot illustrating the reduced fouling of a treated membraneprepared by the methods of the present invention compared to anuntreated membrane.

DETAILED DESCRIPTION OF THE INVENTION

Other than in any operating examples, or where otherwise indicated, allnumbers expressing quantities of ingredients, reaction conditions, andso forth used in the specification and claims are to be understood asbeing modified in all instances by the term “about”. Accordingly, unlessindicated to the contrary, the numerical parameters set forth in thefollowing specification and attached claims are approximations that mayvary depending upon the desired properties to be obtained by the presentinvention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should at least be construed in light of thenumber of reported significant digits and by applying ordinary roundingtechniques.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the invention are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contain certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements.

Also, it should be understood that any numerical range recited herein isintended to include all sub-ranges subsumed therein. For example, arange of “1 to 10” is intended to include all sub-ranges between (andincluding) the recited minimum value of 1 and the recited maximum valueof 10, that is, having a minimum value equal to or greater than 1 and amaximum value of equal to or less than 10.

As used in this specification and the appended claims, the articles “a”,“an”, and “the” include plural referents, unless expressly andunequivocally limited to one referent.

The various embodiments and examples of the present invention aspresented herein are each understood to be non-limiting with respect tothe scope of the invention.

The present invention is directed to a method for treating a surface ofa filled microporous membrane. The microporous membrane comprises apolyolefinic polymeric matrix, finely divided, particulate,substantially water-insoluble inorganic filler distributed throughoutthe matrix, and a network of interconnecting pores communicatingthroughout the microporous membrane. The method comprises sequentially(1) contacting the membrane with a first treatment compositioncomprising an epoxy-silane compound having at least one epoxy group andat least one silane group, wherein the epoxy-silane compound is inintimate contact with the inorganic filler present in the matrix; (2)subjecting the membrane of (1) to conditions sufficient to effect afirst reaction between the inorganic filler and the silane groups of theepoxy-silane compound, wherein the first reaction effected is at least acondensation reaction; (3) contacting the membrane of (2) with a secondtreatment composition comprising polyalkylene polyamine, an aminefunctional polysaccharide and/or an amino silane; and (4) subjecting themembrane of (3) to conditions sufficient to effect a second reaction,wherein the second reaction effected is at least an epoxy ring-openingreaction.

As used herein, “microporous material” or “microporous membrane” or“microporous sheet” means a material having a network of interconnectingpores, wherein, on a treatment-free, coating-free, printing ink-free,impregnant-free, and pre-bonding basis, the pores have a volume averagediameter ranging from 0.001 to 1.0 micrometer, and constitute at least 5percent by volume of the microporous material as discussed herein below.

The polyolefinic polymeric matrix can comprise any of a number of knownpolyolefinic materials known in the art. In some instances, a differentpolymer derived from at least one ethylenically unsaturated monomer maybe used in combination with the polyolefinic polymers. Suitable examplesof such polyolefinic polymers can include, but are not limited to,polymers derived from ethylene, propylene, and/or butene, such aspolyethylene, polypropylene, and polybutene. High density and/orultrahigh molecular weight polyolefins, such as high densitypolyethylene, are also suitable. The polyolefin matrix also can comprisea copolymer, for example, a copolymer of ethylene and butene or acopolymer of ethylene and propylene.

Non-limiting examples of ultrahigh molecular weight (UHMW) polyolefincan include essentially linear UHMW polyethylene (PE) or polypropylene(PP). Inasmuch as UHMW polyolefins are not thermoset polymers having aninfinite molecular weight, they are technically classified asthermoplastic materials.

The ultrahigh molecular weight polypropylene can comprise essentiallylinear ultrahigh molecular weight isotactic polypropylene. Often, thedegree of isotacticity of such polymer is at least 95 percent, e.g., atleast 98 percent.

While there is no particular restriction on the upper limit of theintrinsic viscosity of the UHMW polyethylene, in one non-limitingexample, the intrinsic viscosity can range from 18 to 39deciliters/gram, e.g., from 18 to 32 deciliters/gram. While there is noparticular restriction on the upper limit of the intrinsic viscosity ofthe UHMW polypropylene, in one non-limiting example, the intrinsicviscosity can range from 6 to 18 deciliters/gram, e.g., from 7 to 16deciliters/gram.

For purposes of the present invention, intrinsic viscosity is determinedby extrapolating to zero concentration the reduced viscosities or theinherent viscosities of several dilute solutions of the UHMW polyolefinwhere the solvent is freshly distilled decahydronaphthalene to which 0.2percent by weight, 3,5-di-tert-butyl-4-hydroxyhydrocinnamic acid,neopentanetetrayl ester [CAS Registry No. 6683-19-8] has been added. Thereduced viscosities or the inherent viscosities of the UHMW polyolefinare ascertained from relative viscosities obtained at 135° C. using anUbbelohde No. 1 viscometer in accordance with the general procedures ofASTM D 4020-81, except that several dilute solutions of differingconcentration are employed.

The nominal molecular weight of UHMW polyethylene is empirically relatedto the intrinsic viscosity of the polymer in accordance with thefollowing equation:

M=5.37×10⁴[{acute over (η)}]^(1.37)

wherein M is the nominal molecular weight and [{acute over (η)}] is theintrinsic viscosity of the UHMW polyethylene expressed indeciliters/gram. Similarly, the nominal molecular weight of UHMWpolypropylene is empirically related to the intrinsic viscosity of thepolymer according to the following equation:

M=8.88×10⁴[{acute over (η)}]^(1.25)

wherein M is the nominal molecular weight and [{acute over (η)}] is theintrinsic viscosity of the UHMW polypropylene expressed indeciliters/gram.

A mixture of substantially linear ultrahigh molecular weightpolyethylene and lower molecular weight polyethylene can be used. Incertain embodiments, the UHMW polyethylene has an intrinsic viscosity ofat least 10 deciliters/gram, and the lower molecular weight polyethylenehas an ASTM D 1238-86 Condition E melt index of less than 50 grams/10minutes, e.g., less than 25 grams/10 minutes, such as less than 15grams/10 minutes, and an ASTM D 1238-86 Condition F melt index of atleast 0.1 gram/10 minutes, e.g., at least 0.5 gram/10 minutes, such asat least 1.0 gram/10 minutes. The amount of UHMW polyethylene used (asweight percent) in this embodiment is described in column 1, line 52 tocolumn 2, line 18 of U.S. Pat. No. 5,196,262, which disclosure isincorporated herein by reference. More particularly, the weight percentof UHMW polyethylene used is described in relation to FIG. 6 of U.S.Pat. No. 5,196,262; namely, with reference to the polygons ABCDEF, GHCIor JHCK of FIG. 6, which Figure is incorporated herein by reference.

The nominal molecular weight of the lower molecular weight polyethylene(LMWPE) is lower than that of the UHMW polyethylene. LMWPE is athermoplastic material and many different types are known. One method ofclassification is by density, expressed in grams/cubic centimeter androunded to the nearest thousandth, in accordance with ASTM D 1248-84(Reapproved 1989). Non-limiting examples of the densities are found inthe following table.

Type Abbreviation Density, g/cm³ Low Density PE LDPE 0.910-0.925 MediumDensity PE MDPE 0.926-0.940 High Density PE HDPE 0.941-0.965

Any or all of the polyethylenes listed in the table above may be used asthe LMWPE in the matrix of the microporous material. HDPE may be usedbecause it can be more linear than MDPE or LDPE. Processes for makingthe various LMWPE's are well known and well documented. They include thehigh-pressure process, the Phillips Petroleum Company process, theStandard Oil Company (Indiana) process, and the Ziegler process. TheASTM D 1238-86 Condition E (that is, 190° C. and 2.16 kilogram load)melt index of the LMWPE is less than about 50 grams/10 minutes. Often,the Condition E melt index is less than about 25 grams/10 minutes. TheCondition E melt index can be less than about 15 grams/10 minutes. TheASTM D 1238-86 Condition F (that is, 190° C. and 21.6 kilogram load)melt index of the LMWPE is at least 0.1 gram/10 minutes. In many cases,the Condition F melt index is at least 0.5 gram/10 minutes, such as atleast 1.0 gram/10 minutes.

The UHMWPE and the LMWPE may together constitute at least 65 percent byweight, e.g., at least 85 percent by weight, of the polyolefin polymerof the microporous material. Also, the UHMWPE and LMWPE together mayconstitute substantially 100 percent by weight of the polyolefin polymerof the microporous material.

In a particular embodiment of the present invention, the polyolefinicpolymeric matrix can comprise a polyolefin comprising ultrahighmolecular weight polyethylene, ultrahigh molecular weight polypropylene,high density polyethylene, high density polypropylene, or mixturesthereof.

If desired, other thermoplastic organic polymers also may be present inthe matrix of the microporous material provided that their presence doesnot materially affect the properties of the microporous materialsubstrate in an adverse manner. The amount of the other thermoplasticpolymer which may be present depends upon the nature of such polymer.Non-limiting examples of thermoplastic organic polymers that optionallymay be present in the matrix of the microporous material include lowdensity polyethylene, high density polyethylene,poly(tetrafluoroethylene), polypropylene, copolymers of ethylene andpropylene, copolymers of ethylene and acrylic acid, and copolymers ofethylene and methacrylic acid. If desired, all or a portion of thecarboxyl groups of carboxyl-containing copolymers can be neutralizedwith sodium, zinc, or the like. Generally, the microporous materialcomprises at least 70 percent by weight of UHMW polyolefin, based on theweight of the matrix. In a non-limiting embodiment, the above-describedother thermoplastic organic polymer are substantially absent from thematrix of the microporous material.

The microporous membranes of the present invention further comprisefinely divided, particulate, substantially water-insoluble inorganicfiller distributed throughout the matrix.

The inorganic filler can include any of a number of inorganic fillersknown in the art, provided that the filler is capable of undergoing acondensation reaction with silane present in at least the firsttreatment composition. The filler should be finely divided andsubstantially water insoluble to permit uniform distribution throughoutthe polyolefinic polymeric matrix during manufacture of the microporousmaterial. Generally, the inorganic filler is selected from the groupconsisting of silica, alumina, calcium oxide, zinc oxide, magnesiumoxide, titanium oxide, zirconium oxide, and mixtures thereof.

The finely divided substantially water-insoluble filler may be in theform of ultimate particles, aggregates of ultimate particles, or acombination of both. At least about 90 percent by weight of the fillerused in preparing the microporous material has gross particle sizes inthe range of from 5 to about 40 micrometers, as determined by the use ofa laser diffraction particle size instrument, LS230 from BeckmanCoulton, capable of measuring particle diameters as small as 0.04micron. Typically, at least 90 percent by weight of the filler has grossparticle sizes in the range of from 10 to 30 micrometers. The sizes ofthe filler agglomerates may be reduced during processing of theingredients used to prepare the microporous material. Accordingly, thedistribution of gross particle sizes in the microporous material may besmaller than in the raw filler itself.

As mentioned previously, the filler particles are substantiallywater-insoluble, and also can be substantially insoluble in any organicprocessing liquid used to prepare the microporous material. This canfacilitate retention of the filler in the microporous material.

In addition to the fillers, other finely divided particulatesubstantially water-insoluble materials optionally may also be employed.Non-limiting examples of such optional materials can include carbonblack, charcoal, graphite, iron oxide, copper oxide, antimony oxide,molybdenum disulfide, zinc sulfide, barium sulfate, strontium sulfate,calcium carbonate, and magnesium carbonate. In one non-limitingembodiment, silica and any of the aforementioned optional fillermaterials can comprise the filler.

The filler typically has a high surface area allowing the filler tocarry much of the processing plasticizer used to form the microporousmaterial. High surface area fillers are materials of very small particlesize, materials that have a high degree of porosity, or materials thatexhibit both characteristics. The surface area of the filler particlescan range from 20 to 900 square meters per gram, e.g., from 25 to 850square meters per gram, as determined by the Brunauer, Emmett, Teller(BET) method according to ASTM C 819-77 using nitrogen as the adsorbatebut modified by outgassing the system and the sample for one hour at130° C. Prior to nitrogen sorption, filler samples are dried by heatingto 160° C. in flowing nitrogen (PS) for 1 hour.

In a particular embodiment of the present invention, the inorganicfiller comprises silica, such as precipitated silica, silica gel, orfumed silica.

Silica gel is generally produced commercially by acidifying an aqueoussolution of a soluble metal silicate, e.g., sodium silicate at low pHwith acid. The acid employed is generally a strong mineral acid, such assulfuric acid or hydrochloric acid, although carbon dioxide can be used.Inasmuch as there is essentially no difference in density between thegel phase and the surrounding liquid phase while the viscosity is low,the gel phase does not settle out, that is to say, it does notprecipitate. Consequently, silica gel may be described as anon-precipitated, coherent, rigid, three-dimensional network ofcontiguous particles of colloidal amorphous silica. The state ofsubdivision ranges from large, solid masses to submicroscopic particles,and the degree of hydration from almost anhydrous silica to softgelatinous masses containing on the order of 100 parts of water per partof silica by weight.

Precipitated silica generally is produced commercially by combining anaqueous solution of a soluble metal silicate, ordinarily alkali metalsilicate such as sodium silicate, and an acid so that colloidalparticles of silica will grow in a weakly alkaline solution and becoagulated by the alkali metal ions of the resulting soluble alkalimetal salt. Various acids may be used, including but not limited tomineral acids. Non-limiting examples of acids that can be used includehydrochloric acid and sulfuric acid, but carbon dioxide can also be usedto produce precipitated silica. In the absence of a coagulant, silica isnot precipitated from solution at any pH. In a non-limiting embodiment,the coagulant used to effect precipitation of silica may be the solublealkali metal salt produced during formation of the colloidal silicaparticles, or it may be an added electrolyte, such as a solubleinorganic or organic salt, or it may be a combination of both.

Precipitated silica can be described as precipitated aggregates ofultimate particles of colloidal amorphous silica that have not at anypoint existed as macroscopic gel during the preparation. The sizes ofthe aggregates and the degree of hydration may vary widely. Precipitatedsilica powders differ from silica gels that have been pulverized in thatthe precipitated silica powders generally have a more open structure,that is, a higher specific pore volume. However, the specific surfacearea of precipitated silica, as measured by the Brunauer, Emmet, Teller(BET) method using nitrogen as the adsorbate, is often lower than thatof silica gel.

Many different precipitated silicas can be employed as the filler usedto prepare the microporous material. Precipitated silicas are well-knowncommercial materials, and processes for producing them are described indetail in many United States patents, including U.S. Pat. Nos.2,940,830, 2,940,830, and 4,681,750. The average ultimate particle size(irrespective of whether or not the ultimate particles are agglomerated)of precipitated silicas used is generally less than 0.1 micrometer,e.g., less than 0.05 micrometer or less than 0.03 micrometer, asdetermined by transmission electron microscopy. Non-limiting examples ofsuitable precipitated silicas include those sold under the Hi-Sil®tradename by PPG Industries, Inc.

The inorganic filler particles can constitute from 10 to 90 percent byweight of the microporous membrane. For example, such filler particlescan constitute from 25 to 90 percent by weight of the microporousmembrane, such as from 30 percent to 90 percent by weight of themicroporous membrane, or from 40 to 90 percent by weight of themicroporous membrane, or from 50 to 90 percent by weight of themicroporous membrane, and even from 60 percent to 90 percent by weightof the microporous membrane. The filler typically is present in themicroporous membrane of the present invention in an amount ranging from50 percent to about 85 percent by weight of the microporous membrane.Often, the weight ratio of filler to polyolefin in the microporousmaterial ranges from 0.5:1 to 10:1, such as 1.7:1 to 3.5:1.Alternatively, the weight ratio of filler to polyolefin in themicroporous material may be greater than 4:1. It is contemplated thathigher levels of filler may be employed, as such levels of filler wouldprovide higher surface area available for condensation reactions withthe treatment compositions.

The microporous material used in the membrane of the present inventionfurther comprises a network of interconnecting pores communicatingthroughout the microporous material.

On a treatment-free, coating free, or impregnant-free basis, such porescan comprise at least 5 percent by volume, e.g., from at least 5 to 95percent by volume, or from at least 15 to 95 percent by volume, or fromat least 20 to 95 percent by volume, or from at least 25 to 95 percentby volume, or from 35 to 70 percent by volume of the microporousmaterial. Often, the pores comprise at least 35 percent by volume, oreven at least 45 percent by volume of the microporous material. Suchhigh porosity provides higher surface area throughout the microporousmaterial, which in turn facilitates removal of contaminants from a fluidstream and higher flux rates of a fluid stream through the membrane.

As used herein and in the claims, the porosity (also known as voidvolume) of the microporous material, expressed as percent by volume, isdetermined according to the following equation:

Porosity=100[1−d ₁ /d ₂]

wherein d₁ is the density of the sample, which is determined from thesample weight and the sample volume as ascertained from measurements ofthe sample dimensions, and d₂ is the density of the solid portion of thesample, which is determined from the sample weight and the volume of thesolid portion of the sample. The volume of the solid portion of thesample is determined using a Quantachrome Stereopycnometer (QuantachromeCorp.) in accordance with the accompanying operating manual.

Porosity also can be measured using a Gurley Densometer, model 4340,manufactured by GPI Gurley Precision Instruments of Troy, N.Y. Theporosity values reported are a measure of the rate of air flow through asample or it's resistance to an air flow through the sample. The unit ofmeasure for this method is a “Gurley second” and represents the time inseconds to pass 100 cc of air through a 1 inch square area using apressure differential of 4.88 inches of water. Lower values equate toless air flow resistance (more air is allowed to pass freely). Forpurposes of the present invention, the measurements are completed usingthe procedure listed in the manual for MODEL 4340 Automatic Densometer.

The volume average diameter of the pores of the microporous material canbe determined by mercury porosimetry using an Autopore III porosimeter(Micromeritics, Inc.) in accordance with the accompanying operatingmanual. The volume average pore radius for a single scan isautomatically determined by the porosimeter. In operating theporosimeter, a scan is made in the high pressure range (from 138kilopascals absolute to 227 megapascals absolute). If approximately 2percent or less of the total intruded volume occurs at the low end (from138 to 250 kilopascals absolute) of the high pressure range, the volumeaverage pore diameter is taken as twice the volume average pore radiusdetermined by the porosimeter. Otherwise, an additional scan is made inthe low pressure range (from 7 to 165 kilopascals absolute) and thevolume average pore diameter is calculated according to the equation:

d=2[v ₁ r ₁ /w ₁ +v ₂ r ₂ /w ₂ ]/[v ₁ /w ₁ +v ₂ /w ₂]

wherein d is the volume average pore diameter, v₁ is the total volume ofmercury intruded in the high pressure range, v₂ is the total volume ofmercury intruded in the low pressure range, r₁ is the volume averagepore radius determined from the high pressure scan, r₂ is the volumeaverage pore radius determined from the low pressure scan, w₁ is theweight of the sample subjected to the high pressure scan, and w₂ is theweight of the sample subjected to the low pressure scan.

In the course of determining the volume average pore diameter of theabove procedure, the maximum pore radius detected is sometimes noted.This is taken from the low pressure range scan, if run; otherwise, it istaken from the high pressure range scan. The maximum pore diameter istwice the maximum pore radius. Inasmuch as some production or treatmentsteps, e.g., coating processes, printing processes, impregnationprocesses and/or bonding processes, can result in the filling of atleast some of the pores of the microporous material, and since some ofthese processes irreversibly compress the microporous material, theparameters in respect of porosity, volume average diameter of the pores,and maximum pore diameter are determined for the microporous materialprior to the application of one or more of such production or treatmentsteps.

To prepare the microporous materials of the present invention, filler,polyolefin polymer (typically in solid form such as powder or pellets),processing plasticizer, and minor amounts of lubricant and antioxidantare mixed until a substantially uniform mixture is obtained. The weightratio of filler to polymer employed in forming the mixture isessentially the same as that of the microporous material substrate to beproduced. The mixture, together with additional processing plasticizer,is introduced to the heated barrel of a screw extruder. Attached to theextruder is a die, such as a sheeting die, to form the desired endshape.

In an exemplary manufacturing process, when the material is formed intoa sheet or film, a continuous sheet or film formed by a die is forwardedto a pair of heated calender rolls acting cooperatively to form acontinuous sheet of lesser thickness than the continuous sheet exitingfrom the die. The final thickness may depend on the desired end-useapplication. The microporous material may have a thickness ranging from0.7 to 18 mil (17.8 to 457.2 microns), such as 0.7 to 15 mil (17.8 to381 microns), or 1 to 10 mil (25.4 to 254 microns), or 5 to 10 mil (127to 254 microns), and demonstrates a bubble point of 1 to 80 psi based onethanol.

Optionally, the sheet exiting the calendar rolls may then be stretchedin at least one stretching direction above the elastic limit. Stretchingmay alternatively take place during or immediately after exiting fromthe sheeting die or during calendaring, or multiple times during themanufacturing process. Stretching may take place before extraction,after extraction, or both. Additionally, stretching may take placeduring the application of the first and/or second treatmentcompositions, described in more detail below. Stretched microporousmaterial substrate may be produced by stretching the intermediateproduct in at least one stretching direction above the elastic limit.Usually, the stretch ratio is at least about 1.1. In many cases, thestretch ratio is at least about 1.5. Preferably, it is at least about 2.Frequently, the stretch ratio is in the range of from about 1.2 to about15. Often, the stretch ratio is in the range of from about 1.5 to about10. Usually, the stretch ratio is in the range of from about 2 to about6.

The temperatures at which stretching is accomplished may vary widely.Stretching may be accomplished at about ambient room temperature, butusually elevated temperatures are employed. The intermediate product maybe heated by any of a wide variety of techniques prior to, during,and/or after stretching. Examples of these techniques include radiativeheating, such as that provided by electrically heated or gas firedinfrared heaters; convective heating, such as that provided byrecirculating hot air; and conductive heating, such as that provided bycontact with heated rolls. The temperatures which are measured fortemperature control purposes may vary according to the apparatus usedand personal preference. For example, temperature-measuring devices maybe placed to ascertain the temperatures of the surfaces of infraredheaters, the interiors of infrared heaters, the air temperatures ofpoints between the infrared heaters and the intermediate product, thetemperatures of circulating hot air at points within the apparatus, thetemperature of hot air entering or leaving the apparatus, thetemperatures of the surfaces of rolls used in the stretching process,the temperature of heat transfer fluid entering or leaving such rolls,or film surface temperatures. In general, the temperature ortemperatures are controlled such that the intermediate product isstretched about evenly so that the variations, if any, in film thicknessof the stretched microporous material are within acceptable limits andso that the amount of stretched microporous material outside of thoselimits is acceptably low. It will be apparent that the temperatures usedfor control purposes may or may not be close to those of theintermediate product itself since they depend upon the nature of theapparatus used, the locations of the temperature-measuring devices, andthe identities of the substances or objects whose temperatures are beingmeasured.

In view of the locations of the heating devices and the line speedsusually employed during stretching, gradients of varying temperaturesmay or may not be present through the thickness of the intermediateproduct. Also, because of such line speeds, it is impracticable tomeasure these temperature gradients. The presence of gradients ofvarying temperatures, when they occur, makes it unreasonable to refer toa singular film temperature. Accordingly, film surface temperatures,which can be measured, are best used for characterizing the thermalcondition of the intermediate product.

These are ordinarily about the same across the width of the intermediateproduct during stretching although they may be intentionally varied, as,for example, to compensate for intermediate product having awedge-shaped cross section across the sheet. Film surface temperaturesalong the length of the sheet may be about the same or they may bedifferent during stretching.

The film surface temperatures at which stretching is accomplished mayvary widely, but in general they are such that the intermediate productis stretched about evenly, as explained above. In most cases, the filmsurface temperatures during stretching are in the range of from about20° C. to about 220° C. Often, such temperatures are in the range offrom about 50° C. to about 200° C. From about 75° C. to about 180° C. ispreferred.

Stretching may be accomplished in a single step or a plurality of stepsas desired. For example, when the intermediate product is to bestretched in a single direction (uniaxial stretching), the stretchingmay be accomplished by a single stretching step or a sequence ofstretching steps until the desired final stretch ratio is attained.Similarly, when the intermediate product is to be stretched in twodirections (biaxial stretching), the stretching can be conducted by asingle biaxial stretching step or a sequence of biaxial stretching stepsuntil the desired final stretch ratios are attained. Biaxial stretchingmay also be accomplished by a sequence of one of more uniaxialstretching steps in one direction and one or more uniaxial stretchingsteps in another direction. Biaxial stretching steps where theintermediate product is stretched simultaneously in two directions anduniaxial stretching steps may be conducted in sequence in any order.Stretching in more than two directions is within contemplation. It maybe seen that the various permutations of steps are quite numerous. Othersteps, such as cooling, heating, sintering, annealing, reeling,unreeling, and the like, may optionally be included in the overallprocess as desired.

Various types of stretching apparatus are well known and may be used toaccomplish stretching of the intermediate product. Uniaxial stretchingis usually accomplished by stretching between two rollers, wherein thesecond or downstream roller rotates at a greater peripheral speed thanthe first or upstream roller. Uniaxial stretching can also beaccomplished on a standard tentering machine. Biaxial stretching may beaccomplished by simultaneously stretching in two different directions ona tentering machine. More commonly, however, biaxial stretching isaccomplished by first uniaxially stretching between two differentiallyrotating rollers as described above, followed by either uniaxiallystretching in a different direction using a tenter machine or bybiaxially stretching using a tenter machine. The most common type ofbiaxial stretching is where the two stretching directions areapproximately at right angles to each other. In most cases where thecontinuous sheet is being stretched, one stretching direction is atleast approximately parallel to the long axis of the sheet (machinedirection) and the other stretching direction is at least approximatelyperpendicular to the machine direction and is in the plane of the sheet(transverse direction).

Stretching the sheets prior to extraction of the processing plasticizerallows for thinner films with larger pore sizes than in microporousmaterials conventionally processed. It is also believed that stretchingof the sheets prior to extraction of the processing plasticizerminimizes thermal shrinkage after processing. It also should be notedthat stretching of the microporous membrane can be conducted at anypoint prior to, during, or subsequent to application of the firsttreatment composition (as described herein below), and/or prior to,during, or subsequent to application of the second treatmentcomposition. Stretching of the microporous membrane can occur once ormultiple times during the treatment process.

The product passes to a first extraction zone where the processingplasticizer is substantially removed by extraction with an organicliquid, which is a good solvent for the processing plasticizer, a poorsolvent for the organic polymer, and more volatile than the processingplasticizer. Usually, but not necessarily, both the processingplasticizer and the organic extraction liquid are substantiallyimmiscible with water. The product then passes to a second extractionzone where the residual organic extraction liquid is substantiallyremoved by steam and/or water. The product is then passed through aforced air dryer for substantial removal of residual water and remainingresidual organic extraction liquid. From the dryer, the microporousmaterial may be passed to a take-up roll, when it is in the form of asheet.

The processing plasticizer has little solvating effect on thethermoplastic organic polymer at 60° C., only a moderate solvatingeffect at elevated temperatures on the order of about 100° C., and asignificant solvating effect at elevated temperatures on the order ofabout 200° C. It is a liquid at room temperature and usually it isprocessing oil, such as paraffinic oil, naphthenic oil, or aromatic oil.Suitable processing oils include those meeting the requirements of ASTMD 2226-82, Types 103 and 104. Those oils which have a pour point of lessthan 22° C., or less than 10° C., according to ASTM D 97-66 (reapproved1978) are used most often. Examples of suitable oils include Shellflex®412 and Shellflex® 371 oil (Shell Oil Co.) which are solvent refined andhydrotreated oils derived from naphthenic crude. It is expected thatother materials, including the phthalate ester plasticizers such asdibutyl phthalate, bis(2-ethylhexyl) phthalate, diisodecyl phthalate,dicyclohexyl phthalate, butyl benzyl phthalate, and ditridecyl phthalatewill function satisfactorily as processing plasticizers.

There are many organic extraction liquids that can be used in theprocess of manufacturing the microporous membrane. Examples of suitableorganic extraction liquids include, but are not limited to,1,1,2-trichloroethylene; perchloroethylene; 1,2-dichloroethane;1,1,1-trichloroethane; 1,1,2-trichloroethane; methylene chloride;chloroform; 1,1,2-trichloro-1,2,2-trifluoroethane; isopropyl alcohol;diethyl ether; acetone; hexane; heptane and toluene. One or moreazeotropes of halogenated hydrocarbons selected fromtrans-1,2-dichloroethylene, 1,1,1,2,2,3,4,5,5,5-decafluoropentane,and/or 1,1,1,3,3-pentafluorobutane also can be employed. Such materialsare available commercially as VERTREL™ MCA (a binary azeotrope of1,1,1,2,2,3,4,5,5,5-dihydrodecafluoropentane andtrans-1,2-dichloroethylene: 62%/38%) and VERTREL™ CCA (a ternaryazeotrope of 1,1,1,2,2,3,4,5,5,5-dihydrodecafluorpentane,1,1,1,3,3-pentafluorbutane, and trans-1,2-dichloroethylene:33%/28%/39%); Vertrel™ SDG (80-83% trans-1,2-dichloroethylene, 17-20%hydrofluorocarbon mixture) all available from MicroCare Corporation.

In the above-described process for producing microporous membrane,extrusion and calendering are facilitated when the filler carries muchof the processing plasticizer. The capacity of the filler particles toabsorb and hold the processing plasticizer is a function of the surfacearea of the filler. Therefore, the filler typically has a high surfacearea as discussed above. Inasmuch as it is desirable to essentiallyretain the filler in the microporous material substrate, the fillershould be substantially insoluble in the processing plasticizer andsubstantially insoluble in the organic extraction liquid whenmicroporous material substrate is produced by the above process. Theresidual processing plasticizer content is usually less than 15 percentby weight of the resulting microporous material and this may be reducedeven further to levels such as less than 5 percent by weight, byadditional extractions using the same or a different organic extractionliquid. The resulting microporous materials may be further processeddepending on the desired application.

As previously mentioned, the method for treating a surface of a filledmicroporous membrane, comprises sequentially (1) contacting the membranewith a first treatment composition comprising an epoxy-silane compoundhaving at least one epoxy group and at least one silane group, whereinthe epoxy-silane compound is in intimate contact with the inorganicfiller present in the matrix; (2) subjecting the membrane of (1) toconditions sufficient to effect a first reaction between the inorganicfiller and the silane groups of the epoxy-silane compound, wherein thefirst reaction effected is at least a condensation reaction; (3)contacting the membrane of (2) with a second treatment compositioncomprising polyalkylene polyamine, an amine functional polysaccharideand/or an amino silane; and (4) subjecting the membrane of (3) toconditions sufficient to effect a second reaction, wherein the secondreaction effected is at least an epoxy ring-opening reaction.

The method comprises contacting the microporous membrane with a firsttreatment composition comprising an epoxy-silane compound having atleast one epoxy group and at least one silane group. The first treatmentcomposition typically is in the form of an aqueous composition. Theaqueous first treatment composition can be an aqueous acidiccomposition. Further, the first treatment composition also may includean alcohol either alone (as the sole solvent) or in combination withwater. The first treatment composition is applied to at least onesurface of the microporous membrane such that the epoxy-silane compoundis in intimate contact with the inorganic filler present in thepolymeric matrix.

As mentioned above, the aqueous first treatment composition can comprisean acid. The acid generally can be present in an amount sufficient tomaintain the isoelectric point of the epoxy silane. Suitable acids foruse in the aqueous first treatment composition can include, but are notlimited to, those selected from the group consisting of acetic acid,hydrochloric acid, sulfuric acid, nitric acid, carbonic acid, lacticacid, citric acid, phosphoric acid, oxalic acid, and mixtures thereof.

The first treatment composition also may comprise an alcohol, either asthe sole solvent or in combination with water. Suitable non-limitingexamples of such alcohols can include ethanol, propanol, isopropanol,butanol, and mixtures thereof.

The first treatment composition also comprises an epoxy-silane compoundhaving at least one epoxy group and at least one silane group present onthe molecule. Non-limiting examples of epoxy-silanes suitable for use asa component in the first treatment composition are those selected fromthe group consisting of di-epoxy functional silanes, epoxy cyclohexylsilanes, epoxy cyclohexylalkyl silanes, glycidoxyalkyl silanes, andmixtures thereof. Non-limiting examples of suitable glycidoxyalkylsilanes are those selected from the group consisting of(3-glycidoxypropyl) trialkoxysilane, (3-glycidoxypropyl)bis(trimethylsiloxy)methylsilane, (3-glycidoxypropyl)dimethylethoxysilane, (3-glycidoxypropyl) methyldiethoxysilane, andmixtures thereof.

The first treatment composition can further comprise a poly(alkoxy)silane. Non-limiting examples of suitable poly(alkoxy) silanes for useas a component in the first treatment composition are those selectedfrom the group consisting of tetraalkoxy silane, trialkoxy alkylsilane,dipodal alkoxysilane, and mixtures thereof. Suitable dipodalalkoxysilanes can include but are not limited to those selected from thegroup consisting of bis(triethoxysilyl)ethane,1,8-bis(triethoxysilyl)octane, 1,2-bis(trimethoxysilyl)decane,bis(trimethoxysilylethyl)benzene, bis(triethoxysilyl)ethylene, andmixtures thereof.

The first treatment composition can be applied to the microporousmembrane by any application means known in the art. For example, thefirst treatment composition can be applied to at least one surface ofthe microporous membrane by immersion, by spray, by dip, and/or by flowor certain application techniques. The first treatment composition maybe applied after plasticizer extraction and either prior to, during, orafter any of the stretching steps. Alternatively, stretching can bedelayed until application of the second treatment solution, as describedbelow. Upon application of the first treatment composition to at leastone surface of the microporous membrane in (1), the membrane of (1) is(2) subjected to conditions sufficient to effect a first reactionbetween the functional groups present on the surface of the inorganicfiller and the silane groups of the epoxy-silane compound. That is, in(2) the membrane of (1) is subjected to conditions sufficient to effectat least a condensation reaction. Such reaction conditions will bediscussed in more detail herein below.

The microporous membrane of (2) then is contacted in (3) with a secondtreatment composition comprising a polyalkylene polyamine, an aminefunctional polysaccharide and/or an amino silane. For purposes of thepresent invention, by “alkylene” is meant a bivalent saturated aliphaticradical (such as ethylene) regarded as being derived from an alkene byopening of the double bond, or from an alkane by removal of two hydrogenatoms from two different carbon atoms. Polyalkylene polyamine is alinear or branched polyamine having more than one alkylene grouppresent, which is free of unsaturation and having at least two aminogroups. Non-limiting examples of suitable polyalkylene polyamines can beselected from the group consisting of C₂ to C₆ alkanediamine,diethylenetriamine, polyethylene imine, and mixtures thereof.

In a particular embodiment of the present invention, the secondtreatment composition comprises a polyalkylene polyamine which is alinear or branched polyethylene imine. In lieu of or in combination withthe aforementioned polyalkylene polyamine(s), the second treatmentcomposition can comprise an amine-functional polysaccharide, such aspolyglucosamine (e.g., chitosan).

Any of the above-mentioned second treatment compositions also cancomprise any of a number of known amino silanes. Such amino silanes caninclude but are not limited to diamino functional silanes, triaminofunctional silanes, secondary amino functional silanes, tertiary aminofunctional silanes, quaternary amino functional silanes, silanefunctional polyamines, and dipodal amino functional silanes.Non-limiting examples of suitable amino silanes can includeaminopropyltriethoxysilane, aminopropyltrimethoxysilane,aminobutyltriethoxysilane, aminophenyltrimethoxysilane,3-aminopropyltris (methoxyethoxyethoxy) silane,11-aminoundecyltriethoxysilane, 2-(4-pyridylethyl)triethoxysilane,aminopropylsilanetriol, 3-(m-aminophenoxy)propyltrimethoxy silane,3-aminopropylmethyldiethoxysilane, 3-aminopropylmethyldiethoxysilanesilane, 3-aminopropyldimethylethoxysilane,n-(2-aminoethyl)-3-aminopropyltri-ethoxysilane,n-(2-aminoethyl)-3-aminopropyl-silanetriol,n-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane,n-(2-aminoethyl)-3-aminoisobutyl methyldimethoxysilane,bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane,diethylaminomethyltriethoxysilane, n,n-diethyl-3-aminopropyl)trimethoxysilane,3-(n-styrylmethyl-2-aminoethylamino) propyitrimethoxysilanehydrochloride, n-trimethoxysilylpropyl-n,n,n-tri methylammoniumchloride, n-(trimethoxysilylethyl)benzyl-n,n,n trimethylammoniumchloride, bis(methyldiethoxysilylpropyl)amine,ureidopropyltrimethoxysilane, trimethoxysilylpropyl modified(polyethyleneimine), and mixtures of any of the foregoing.

Any of the second treatment compositions previously described also cancomprise one or more of the following amino compounds: C₂-C₆alkanediamine, polyethylenimine, 1,3-bis(aminomethyl)cyclohexane,ethylenediamine, diethylenetriamine, triethylenetetramine,hexamethylenediamine, 2-methyl-1,5-pentanediamine-,1,6-hexamethylenediamine,2-heptyl-3,4-bis(9-aminononyl)-1-pentylcyclohexane(dimeryidiamine),polyglucosamine, polyoxyalkylene diamine, e.g. polyoxypropylene diamine,isophoronediamine, norbornodiamine,2.5(2.6)-bis(aminomethyl)bicyclo(2.2.1) heptane,4,4′-dicyclohexylmethane diamine, 1,4-diaminocyclohexane,menthanediamine, and/or bis(aminomethyl)cyclohexane.

In a particular embodiment of the present invention, the secondtreatment composition comprises (i) a polyamine selected from the groupconsisting of polyethylene imine, polyglucosamine and mixtures thereof;and/or (ii) 3-aminopropyltriethoxy silane.

Also, the second treatment composition which is applied to themicroporous membrane of (2) in accordance with the method of the presentinvention can further comprise at least one nonionic surfactant asdescribed immediately below, as well as a polyalkylene oxazoline such aspolyethylene oxazoline.

Non-limiting examples of suitable nonionic surfactants for use in thesecond treatment composition used in the method of the present inventioncan include but are not limited to polyalkylene oxide alkyl etherswherein the alkyl group can be straight chain or branched having a chainlength of from C₆ to C₂₂; polyalkylene oxide alkyl esters wherein thealkyl group can be straight chain or branched having a chain length offrom C₆ to C₂₂, organic amines with straight or branched carbon chainsfrom C₆ to C₂₂ having the general formula R*NR′R″ wherein R* can be fromC₈ to C₂₂ alkyl and R′ and R″ can each independently be H or C₁ to C₄alkyl such that the molecule can be substantially soluble orsubstantially emulsifiable in water, for example octadecylamine;tertiary amines with carbon chains from C₆ to C₂₂, polyethyleneimines;polyacrylamides; glycols and alcohols with straight chain or branchedalkyl from C₆ to C₂₂ that can form ester linkage (—SiOC—), polyvinylalcohol; and mixtures thereof.

The nonionic surfactant also can be chosen from polyalkylene oxideethers such as polypropylene oxide ethers and polyethylene oxide etherssuch as but not limited to hexaethylene glycol monododecylether,hexaethylene glycol monohexadecylether, hexaethylene glycolmonotetradecylether, hexaethylene glycol monooctadecylether,heptaethylene glycol monododecylether, heptaethylene glycolmonohexadecylether, heptaethylene glycol monotetradecylether,heptaethylene glycol monooctadecylether, nonaethylene glycolmonododecylether, octaethylene glycol monododecylether; polyalkyleneoxide esters, for example polypropylene oxide esters and polyethyleneoxide esters such as but not limited to hexaethylene glycolmonododecylester, hexaethylene glycol monohexadecylester, hexaethyleneglycol monotetradecylester, hexaethylene glycol monooctadecylester,heptaethylene glycol monododecylester, heptaethylene glycolmonohexadecylester, heptaethylene glycol monotetradecylester,heptaethylene glycol monooctadecylester, nonaethylene glycolmonododecylester, octaethylene glycol monododecylester; polysorbateesters such as polyoxyethylene sorbitan mono fatty acid esters includingbut not limited to polyoxyethylene sorbitan mono palmitate,polyoxyethylene sorbitan mono oleate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan difatty acid esters such aspolyoxyethylene sorbitan dipalmitate, polyoxyethylene sorbitan dioleate,polyoxyethylene sorbitan distearate, polyoxyethylene sorbitanmonopalmitate monooleate, polyoxyethylene sorbitan tri fatty acid esterssuch as but not limited to polyoxyethylene sorbitan tristearate; andmixtures thereof.

In a particular embodiment, the second treatment composition used in themethod of the present invention comprises a nonionic surfactant selectedfrom block copolymers based on poly(ethylene glycol), for example, blockcopolymers of poly(propylene glycol) and poly(ethylene glycol), (such asthe triblock copolymer PLURONIC® 17R2 which is commercially availablefrom BASF Corporation); cetylstearyl alcohol; polyethylene glycol andderivatives thereof, for example, polyoxyethylene octyl phenyl ether;polyalkyl glycols; cetyl alcohol; cocamide mono- or di-ethanolamine;decyl gylcoside; octylphenoxypolyethoxyethanol; isocetyl alcohol; laurylglucoside; monolaurin; fatty alcohol polyglycol ethers; polyglycolethers; polyethylene glycol derivatives of mono or diglycerides; monoand poly glycerol derivatives, for example, polyglycerolpolyricinoleate; sorbitan esters; polysorbates and oxidizedpolyethylene. Mixtures of any of the aforementioned nonionic surfactantscan be used.

The second treatment composition can be applied to the membrane of (2)by any art recognized application methods, such as any of thosedescribed above with reference to the first treatment composition.

The method for treating a surface of a filled microporous membrane inaccordance with the present invention further comprises (4) subjectingthe membrane of (3) to conditions sufficient to effect a secondreaction, wherein the second reaction effected is at least an epoxyring-opening reaction.

In one embodiment, the first reaction of (2) is a condensation reactioneffected by contacting the membrane of (1) with a basic solution suchthat the basic solution is in intimate contact with the inorganicfiller. Generally, the basic solution can comprise any of the well-knownbases. In a particular embodiment of the present invention, the firstreaction of (2) (a condensation reaction) is achieved by contacting themembrane of (1) with a base selected from ammonium hydroxide, sodiumhydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide,and mixtures thereof. In this embodiment of the present invention, thesecond reaction of (4) (at least an epoxy ring-opening reaction where atleast one of the amino groups of the polyamine and/or the amino silanereacts with at least one epoxy group of the epoxy silane present in thefirst treatment composition) is effected by contacting the membrane of(3) with an acidic solution. The acidic solution can comprise any of theart recognized acids. In a particular embodiment, the acid solutioncomprises an acid selected from acetic acid, hydrochloric acid, sulfuricacid, nitric acid, carbonic acid, citric acid, phosphoric acid, oxalicacid, and mixtures thereof. This method is hereinafter referred to asthe “wet method”. In the wet method, the first and second treatmentcompositions can be applied to one or more surfaces of the microporousmembrane as described above in regards to the dry method, or the firstand second compositions can be passed through the microporous membraneat elevated pressure. In the wet method, one or both of the firstreaction of (2) and the second reaction of (4) can occur at ambienttemperature. This wet method can be effectively used to treat orreclaim/clean a microporous membrane which is in the form of a sheet orwhen the microporous membrane is a component of an existing orpre-fabricated separation device, such as the filter membrane componentof a spiral wound or pleated filter device, or a separation membrane asa component of a battery (i.e., a battery separator).

In another embodiment of the present invention, one or both of the firstreaction of (2) and the second reaction of (4) is/are effected byexposing the treated microporous membrane to elevated temperatures. Thismethod is hereinafter referred to as the “dry method”. The temperaturegenerally ranges from 50° C. to 145° C. Such temperatures are sufficientto effect at least a condensation reaction in (2) and at least an epoxyring-opening reaction in (4). The dry method is particularly useful fortreatment of microporous membranes in the form of a sheet. The drymethod can be initiated on a microporous membrane prior to anystretching, or after machine direction stretching and prior to a crossdirection stretching, or the dry method can be initiated on amicroporous membrane that has already undergone biaxial stretching.Also, when the dry method is employed during (2), the microporousmembrane may be stretched during the drying/heating step in addition toor instead of stretching prior to treatment with the first treatmentcomposition. During application of the first and second treatmentcompositions in the dry method, it should be noted that the microporousmembrane to which the respective treatment compositions are appliedshould be held dimensionally stable during said applications. Further,during the dry method drying/heating steps, the membrane typically isheld under tension in order to prevent/minimize shrinkage, regardless ofwhether the stretching is occurring simultaneously.

It should be noted herein that the wet and dry method steps can becombined, if desired. For example, the first reaction step may beeffected by the dry method, while the second reaction step can beeffected by the wet method, or vice versa.

The present invention also provides microporous membranes prepared byany of the various methods described above.

The methods for treating a surface of a filled microporous membrane inaccordance with the present invention differ significantly from theheretofore known methods where conventional hydrophilic coatings areapplied to the surfaces of the microporous membranes. In the methods ofthe present invention, the components of the first and second treatmentcompositions interact chemically with the inorganic filler at allexposed surfaces in and on the membrane, including within the pores. Thecomponents are reacted via condensation to form a permanent surfacewhich is then further condensed/reacted with amine functional and acidcomponents to impart hydrophilic character over the entire membrane,including the surfaces of the pores without occluding the pores. Suchmethods result in the treatment being bound to the surface of themembrane and the interior of the pores via covalent interaction with theinorganic filler particles. Hence, the treatment is not removed bynormal physical or chemical usage (e.g., by cleaning with a basiccleaning solution). It has been found that, when used in oil-waterseparation applications, the membranes prepared by the methods of thepresent invention exhibit a longer practical lifetime as evidenced bydecreased fouling, improved flux rates over extended periods of time,and robustness against cleaning procedures as compared to an equivalent,untreated membrane. Such membranes also can demonstrate lower shrinkage(i.e., the membranes maintain the integrity of the pores) as compared toan equivalent untreated membrane. This is particularly true for themembranes of the present invention, which are prepared using the drymethod as mentioned above.

The present invention is more particularly described in the followingexamples which are intended to be illustrative only, since numerousmodifications and variations therein will be apparent to those skilledin the art.

EXAMPLES Part 1. Substrate Preparation:

A membrane was prepared in accordance with Example 4 in Publication No.US2013/0228529A1. The extruded sheet was then stretched in both theMachine and Cross Machine Directions. Machine Direction stretching wascarried out at a temperature of 270° F. with a slow draw roll set at 15feet per minute (FPM) and fast draw roll set at 28 FPM. Cross Machinestretching was carried out at a temperature of 270° F. and a stretchingratio of 2 to 1. This membrane was used in the preparation of all of thefollowing examples and comparative examples.

Part 2. Preparation of Treatment Solutions: First Treatment SolutionCompositions

Solutions A through D: For each composition listed in Table 1 below, apolyethylene beaker fitted with an air-driven paddle stirrer was chargedwith the specified amount of water and 2-butoxyethanol, then stirred for5 minutes. The acetic acid was added and allowed to stir for 5 minutes.The 3-glycidoxypropyltrimethoxysilane, then tetraethoxysilane (whereindicated) were added, stirring for 15 minutes after each addition. ThepH of each solution was between 3-4.

TABLE 1 Solutions Ingredients (parts by weight) A B C D 2-Butoxyethanol5.0 4.2 5.0 4.2 Water 79.2 65.8 77.4 64.9 Acetic acid 2.0 2.0 2.0 1.73-Glycidoxypropyltrimethoxysilane 13.8 8.0 13.8 27.7 Tetraethoxysilane2.0 1.8 1.5

Second Treatment Solution Compositions

Solution E: Two parts glacial acetic acid was mixed for 30 minutes in 97parts water. To this was added one part chitosan (85% deacetylate fromshrimp) and the solution was stirred for 4 hours prior to use.

Solutions F through J: For each composition listed in Table 2 below, apolyethylene beaker fitted with air-driven paddle stirrer was chargedwith cool water and agitated to generate approximately a 1 inch vortex.The specified amount of poly(2-ethyl-2-oxazoline) was added and stirredfor 4 hours. The surfactant and 2-butoxyethanol were added and thesolution was stirred for an additional 30 minutes. The3-aminopropyltriethoxysilane then was added and the solution stirred for15 minutes. The trimethoxysilylpropyl-polyethyleneimine solution wasadded to the main mix container and stirred for 5 minutes prior to use.

TABLE 2 Ingredients (parts by Solutions weight) F G H I J Water 81.981.9 81.9 77.3 63.7 2-butoxyethanol 5.4 5.4 5.4 5.1 4.2 PLURONIC ® 17R2¹0.9 0.9 0.9 0.9 0.7 Poly(2-ethyl-2-oxazoline)² 1.8 1.8 1.8 1.7 1.43-aminopropyltriethoxysilane 10.0 7.5 15.0 trimethoxysilylpropyl- 10.07.5 15.0 polyethylenimine³ Poly(ethyleneimine)⁴ 10.0 ¹A block copolymersurfactant with reported weight average M_(w) of 2150, available fromBASF Corporation. ²Average Molecular weight of 50,000, supplied bySigmaAldrich. ³A 50% solution in isopropyl alcohol, sold under theproduct code SSP-060 by Gelest, Inc. ⁴A branched polyethyleneimine withreported average Mn of 10,000 and Mw of 25,000 purchased fromSigma-Aldrich under the product number 408727.

Solution K: A basic neutralization solution was prepared by combiningwater (65.8 parts by weight), 2-butoxyethanol (4.2 parts by weight) and29% aqueous ammonium hydroxide (1.0 parts by weight) and stirring for aminimum of 10 minutes prior to use.

Solution L: An acidic neutralization solution was prepared by combiningwater (65.8 parts by weight), 2-butoxyethanol (4.2 parts by weight) andglacial acetic acid (2.0 parts by weight), and stirring for a minimum of10 minutes prior to use.

Control Solution M: A hydrophilic coating solution was prepared bydispersing SELVOL® 325 polyvinyl alcohol (6 g), supplied by SekisuiSpecialty Chemicals America, in cool water (294 g) under mild agitationin a 600 mL beaker. The solution then was heated to a temperature of190° F. and stirred for 30 minutes, then allowed to cool to roomtemperature with stirring prior to use.

Control Solution N: A hydrophilic coating solution was prepared inaccordance with Part III, Example A in US Publication No.2014/0069862A1, but using 10 g of the polyethyloxazoline in theformulation.

Part 3. Sample Preparation:

For all examples and comparative examples described below, a sheet ofthe microporous membrane described in Part 1 was cut to sample membranesheets sized to approximately 7×7 inches and clamped to the outerperimeter of a 5 inch×5 inch metal square frame, fabricated from ¾ inchsquare tubular metal stock, with excess slack removed. The frame withfitted membrane sheet was placed on a flat counter with the continuoussheet or top side facing up. This upward orientation was maintainedthrough each of the treatment steps.

Part 3A. Neutralization Conditions after First and Second TreatmentSteps:

Treatment solutions were applied to the top side of the framed membranein the order indicated in Table 3 below. For each example, the firsttreatment solution was liberally applied to the top side of the sheetusing a disposable dropper until the liquid was clearly wet through thesheet as determined by observation of constant sheet transparency uponaddition of more solution. Total solution application and wet throughrequired approximately one minute to complete. Excess free liquid wasgently wiped from all membrane surfaces and the framed membrane wasplaced in an air tight plastic bag for the time specified to preventevaporation. The assembly was removed from the bag and each subsequenttreatment was applied in sequence until the liquid no longer absorbedinto the membrane as evidenced by standing liquid on the surface, whichwas then wiped off and followed by the specified hold time in an airtight plastic bag between each step. The treated membranes were keptmoist in the bag until testing.

TABLE 3 Example 1 2 3 First treatment B B B solution Hold time (min) 1515 15 Neutralizing K K K solution Hold time (min) 15 15 15 Secondtreatment I I E solution Hold time 15 240 15 Neutralizing L L 0.2M H₂SO₄solution Hold time (min) 15 15 10Part 3B. Heated Drying Conditions after First and Second TreatmentSteps:

Treatment solutions were applied to the top side of the framed membranein the order indicated in Table 4. For each example, the first treatmentsolution was liberally applied to the top side of the membrane sheetusing a disposable dropper until the liquid was clearly wet through thesheet as determined by observation of constant sheet transparency uponaddition of more solution. Total solution application and wet throughrequired approximately one minute to complete. Any excess free liquidwas gently wiped from all membrane surfaces and the framed membrane wasplaced in a forced air oven for 15 minutes, set at the indicatedtemperature for the time listed in Table 4 below. The framed membranewas placed on the counter top with top side of the sheet facing up andallowed to cool to room temperature. Once cooled to room temperature,the second treatment solution was applied to the top side of the sheetusing the same procedure as above. Any excess free liquid was gentlywiped from all membrane surfaces and the assembly was placed in a forcedair oven for 15 minutes, set at the temperature indicated. The framedmembrane was placed on the counter top with top side of the sheet facingup and allowed to cool to room temperature prior to testing.

TABLE 4 Example 4 5 6 7 8 9 10 First treatment A B B B B C D solutionHold 135 105 135 135 135 135 135 temperature (° C.) Second treatment I IF G H H J solution Hold 135 105 135 135 135 135 135 temperature (° C.)

Part 3C. Example 11

One example was fabricated using heated drying conditions afterapplication of the first treatment solution, and neutralization afterthe second treatment solution as follows: First treatment Solution D wasapplied as described above. The treated membrane assembly was placed ina forced air oven, set at 135° C., for 15 minutes. After the membranecooled to room temperature, second treatment Solution I was applied asdescribed above and the membrane placed in an air tight plastic bag for15 minutes to prevent evaporation. The assembly was removed from thebag, keeping the top side facing up, and acidic Solution L was applieduntil the liquid was no longer absorbed by the membrane, and the excesswas gently wiped off. The framed membrane was placed in an air tightplastic bag for 15 minutes prior to subjecting the material to testingbelow.

Part 3D. COMPARATIVE EXAMPLES

Comparative Examples CE-12 and CE-13 utilize hydrophilic coatings knownin the art as described above. Comparative Examples CE-14 and CE-15represent membranes treated with only one of the first treatmentcomposition or the second treatment composition.

For each of the comparative examples, a treatment solution was firstapplied according to Table 5. Each of the solutions was liberallyapplied to the top side of the sheet using a disposable dropper untiltransparency was unchanged with additional solution. Any excess freeliquid was gently wiped from the membrane surface. The membranes werethen post-treated according to the conditions listed in Table 5. Forthose treated with heat, the framed membrane was placed in a forced airoven, set at 105° C., for 15 minutes. For those comparative examplesfurther treated with neutralization solutions, the framed membrane wasplaced in air tight plastic bag for 15 minutes after the application ofthe first solution. The framed membrane was removed from the bag, andthe specified neutralizing solution was applied until the liquid nolonger absorbed into the membrane as evidenced by standing liquid on thesurface, which was then wiped off. The samples were then placed in anair tight plastic bag again for 15 minutes prior to testing.

TABLE 5 Examples CE-12 CE-13 CE-14 CE-15 Treatment solution M N D DPost-treatment Heat Heat Heat 15 minutes conditions sealed bagNeutralizing — — — K solution Post-treatment — — — 15 minutes conditionssealed bag

Part 4. Physical Properties:

The membranes prepared in Part 3 were tested for the physical propertiesdescribed below.

Gurley: This test was performed only on dry membrane samples. Porositywas determined using a Gurley Precision Densometer, model 4340,manufactured by GPI Gurley Precision Instruments of Troy, N.Y. Thetesting area was 1 in² and the result reported as Gurley seconds per 100cc of air.

Contact angle: was measured on a VCA 2500XE video contact angle system,available from AST Products, Inc. using 1 microliter of ultrapure water.Contact angles were measured on heat treated (i.e., dry) sample.

Thermal shrinkage test: 8 cm by 8 cm sample coupons of the treatedmaterials were placed in an oven at 120° C. for 30 min. All samples wereplaced directly in the oven, either wet or dry depending on the methodof treatment. The samples were removed from the oven and allowed to coolfor 2 min. The resultant samples were measured 3 times in both the cross(CD) and machine (MD) directions, the values averaged and the shrinkagecalculated and reported as a percentage of the original pre-heatedsample coupons.

Dry wet shrinkage test: 8 cm by 8 cm sample coupons of the treatedmaterials were used. For wet samples, the coupons were cut from thefinished membrane and allowed to dry at room temperature overnight. Heattreated (i.e., dry) samples were soaked in deionized water for one hour.Those with water contact angles greater than 10 were pre-wet with a50/50 water/isopropyl alcohol solution, then rinsed with and soaked forone hour in deionized water. After soaking, the samples were removedfrom the water bath and air dried at room temperature overnight. Theresultant samples were measured 3 times in both the cross (CD) andmachine (MD) directions, the values averaged and the shrinkagecalculated and reported as a percentage of the original pre-wet samplecoupons in Table 6.

TABLE 6 Physical properties of treated membranes Wet/Dry Thermal WaterShrinkage shrinkage 120° C. Gurley Contact (%) (%) Example (sec) AngleCD MD CD MD 1 — — 30 20 34 25 2 — — 35 17 Not measured 3 — — 20 22 30 234 122  <10 6 3 2 3 5 71 <10 6 2 1 4 6 59 <10 8 2 1 1 7 53 <10 4 4 0 3 857 <10 12 6 5 0 9 65 <10 10 8 4 1 10 326  <10 2 2 Not measured 11 — — 3414 8 25 CE-12 2389   37 36 16 19 6 CE-13 46 <10 34 12 24 9 CE-14 46 10012 10 Not measured CE-15 — — 30 17 8 25 Untreated 39   113.5 34 16 24 11membrane

Part 5. Performance Testing of Treated Membranes:

Each of the prepared membranes of Part 3 were tested for the followingperformance properties.

Water flux: Water flux was tested with a Sterlitech filter holder with amembrane area of 90 cm². The Sterlitech unit fitted with the membranewas charged with 1 liter of water and sealed. The air pressure was setto 50 psi and the time required for the 1 liter quantity of water topass through the membrane was recorded. The corresponding water flux wascalculated.

Oil resistance: The water-wetted membrane of interest was removed fromthe water flux test equipment above and immediately evaluated for oilresistance. Three drops of Texas crude oil (supplied by Texas Raw Crude,International) were placed on the membrane surface using a disposabledropper. All three drops were allowed to remain undisturbed forapproximately one minute, then wiped off using a paper wipe. If the oildrop penetrated and stained the membrane, the result was given a ratingof 1. If the oil drop remained mostly on the surface but clearly stainedthe membrane, the result was given a rating of 2. If the oil dropremained at the surface, did not penetrate the membrane and/or onlyslightly stained the surface, the result was given a rating of 3.

Oil absorption test: A 2 cm by 2 cm coupon of membrane was completelysubmerged into a 50/50 emulsion of water and Texas crude oil for 24hours. The sample was then removed from the oil bath and all excess oilwiped from the surface. The resultant sample was placed in a beakerfilled with 100 ml of hexane, allowed to soak for 5 minutes and thenremoved. The corresponding oil concentration in the hexane soak wasdetermined with a TD-3100 from Turner Design Hydrocarbon Instruments.

Water/oil extrusion pressure test: A 200 ml quantity of a 50/50 volumeblend of water and Texas crude oil was used for the test along with afilter holder with a membrane area of 90 cm² (available from SterlitechCorporation). Once the unit was fully fitted and charged, the test wasinitiated at a pressure of 5 psi and then the pressure was increased at5 psi increments every 10 minutes. The pressures at which water and thenoil passed through the membrane were recorded. The difference betweenthese two pressures is recorded in Table 7 as AP oil-water.

The performance results presented in Table 7 below illustrate that themicroporous membranes prepared by the methods of the present inventiondemonstrate higher oil resistance and lower oil absorption than otherhydrophilic coatings known in the art (comparative examples). Low APvalues (less than or equal to 5 psi) directly correlate tooil-contaminated permeate in practical use.

TABLE 7 Performance of treated membranes Oil Water flux Oil absorptionΔP oil-water Example (ml/min/cm²) Resistance (mg/cm²) (psi) 1 26.0 2 9.215 2 20.3 3 4.4 15 3 12.5 3 4.0 15 4 11 3 6.6 15 5 16 3 6.5 15 6 11 27.4 10-15 7 23 3 6.7 Not measured 8 20 3 7.7 30 9 8 3 0.8 20 10 3 3 2.720 11 23.7 3 5.9 Not measured CE-12 0.6 2 9.1 N/A¹ CE-13 18.4 1 9.0 5CE-14 23 1 15 5 CE-15 24.5 1 15 5 Untreated 22.4 1 14.5 5 membrane ¹ΔPnot measurable due to very low flux.

Part 6. Treatment and Testing of Fabricated Filtration Cartridge:

The membrane described in Part 1 was assembled into two industrystandard 1812 size spiral wound cartridges with a single leaf design.The cartridges each contained 3.5 ft² of active membrane area with a 35mil (899 micron) thick feed space. One of these cartridges was leftuntreated and the other was treated as follows: The cartridge treatmentsystem comprised an ARO double diaphragm pump, valves, piping, fittings,pressure and flow gauges positioned in a secondary containment base withdimensions 24″×18″. The tallest point of the assembly was 24″. Thesystem was designed to cycle liquids under pressure through an 1812cartridge. One liter of first treatment Solution B was pumped throughthe cartridge for 1 minute at a peak pressure of 20 psi, held in thecartridge for 15 minutes, and drained out by gravity. The cartridge wasnext treated with one liter basic neutralizing solution K, followed byone liter of second treatment Solution I, and finally one literneutralizing solution L. Each of the solutions were pumped through thecartridge for 1 minute at a peak pressure of 20 psi, held in thecartridge for 15 minutes, then drained by gravity. The cartridge wasfinally treated with one liter of water for 15 minutes under continuouspumping prior to testing.

The treated cartridge and the untreated cartridge were each assembledinto an 1812 RO membrane housing with ¼ inch port in the feed inlet. Asalt/oil/water mixture designed to simulate produced water was used forthe testing, the composition of which is detailed in Table 8 below.

TABLE 8 Salt/oil/water Formulation Components (%) Ca(NO₃)₂*4H₂O 3.92MgSO₄ 0.15 NaCl 4.58 NaNO₃ 0.74 FeCl₃(50%) 0.01 K₂CO₃ 0.02 Sodiumdodecylbenzene 0.025 sulfonate Texas Crude Oil 0.25 Water 90.31

The solution was pumped through the cartridge being tested at a feedflow of 3 gallons/minute. The feed return and permeate were directedback into the original sourcing container and the feed pressure, flowand temperature were each recorded with time. An additional 300 ppm ofoil was added every 8 hours throughout the test to simulate constant useconditions. The permeate flow rate was recorded over time and reportedas GFD (Gal/ft²/day). The results are presented graphically in FIG. 1.

The test results presented in FIG. 1 illustrate the reduced fouling of amembrane prepared by the methods of the present invention (incorporatedas a component in a filter cartridge) compared to an untreated membrane(incorporated as a component in an analogous filter cartridge). Thisreduced fouling contributes significantly to a longer useful lifetime ofthe cartridge.

Whereas particular embodiments of this invention have been describedabove for purposes of illustration, it will be evident to those skilledin the art that numerous variations of the details of the presentinvention may be made without departing from the scope of the inventionas defined in the appended claims.

The invention claimed is:
 1. A method for treating a surface of a filledmicroporous membrane, said microporous membrane comprising apolyolefinic polymeric matrix, finely divided, particulate,substantially water-insoluble inorganic filler distributed throughoutthe matrix, and a network of interconnecting pores communicatingthroughout the microporous membrane, said method comprisingsequentially: (1) contacting the membrane with a first treatmentcomposition comprising an epoxy-silane compound having at least oneepoxy group and at least one silane group, wherein the epoxy-silanecompound is in intimate contact with the inorganic filler present in thematrix; (2) subjecting the membrane of (1) to conditions sufficient toeffect a first reaction between the inorganic filler and the silanegroups of the epoxy-silane compound, wherein the first reaction effectedis at least a condensation reaction; (3) contacting the membrane of (2)with a second treatment composition comprising polyalkylene polyamine,an amine functional polysaccharide and/or an amino silane; and (4)subjecting the membrane of (3) to conditions sufficient to effect asecond reaction, wherein the second reaction effected is at least anepoxy ring-opening reaction.
 2. The method of claim 1, wherein the firsttreatment composition is an aqueous composition.
 3. The method of claim2, wherein the first treatment composition is an acidic aqueouscomposition.
 4. The method of claim 1, wherein the first treatmentcomposition comprises an alcohol.
 5. The method of claim 4, wherein thealcohol is selected from the group consisting of ethanol, propanol,isopropanol, butanol, and mixtures thereof.
 6. The method of claim 1,wherein the inorganic filler is selected from the group consisting ofsilica, alumina, calcium oxide, zinc oxide, magnesium oxide, titaniumoxide, zirconium oxide, and mixtures thereof.
 7. The method of claim 6,wherein the inorganic filler comprises silica.
 8. The method of claim 1,wherein the polyalkylene polyamine is selected from the group consistingof C₂-C₆ alkanediamine, diethylenetriamine, polyethylene imine, andmixtures thereof.
 9. The method of claim 8, wherein the polyalkylenepolyamine comprises a linear or branched polyethylene imine.
 10. Themethod of claim 1, wherein the second treatment composition furthercomprises a nonionic surfactant and/or polyalkylene oxazoline.
 11. Themethod of claim 1, wherein the amine-functional polysaccharide ispolyglucosamine.
 12. The method of claim 1, wherein the first treatmentcomposition further comprises poly(alkoxy) silane.
 13. The method ofclaim 1, wherein the epoxy-silane compound is selected from the groupconsisting of di-epoxy functional silanes, epoxy cyclohexylsilanes,epoxy cyclohexylalkyl silanes, glycidoxyalkyl silanes, and mixturesthereof.
 14. The method of claim 13, wherein the epoxy-silane compoundis a glycidoxyalkyl silane selected from the group consisting of(3-glycidoxypropyl) trialkoxysilane, (3-glycidoxypropyl)bis(trimethylsiloxy)methylsilane, (3-glycidoxypropyl)dimethylethoxysilane, (3-glycidoxypropyl) methyldiethoxysilane, andmixtures thereof.
 15. The method of claim 12, wherein the poly(alkoxy)silane is selected from the group consisting of tetraalkoxy silane,trialkoxy alkylsilane, dipodal alkoxysilane, and mixtures thereof. 16.The method of claim 15, wherein the poly(alkoxy) silane is a dipodalalkoxysilane selected from the group consisting ofbis(triethoxysilyl)ethane, 1,8-bis(triethoxysilyl)octane,1,2-bis(trimethoxysilyl)decane, bis(trimethoxysilylethyl)benzene,bis(triethoxysilyl)ethylene, and mixtures thereof.
 17. The method ofclaim 2, wherein the first treatment composition comprises an acidpresent in an amount sufficient to maintain the isoelectric point of theepoxy silane.
 18. The method of claim 17, wherein the acid is selectedfrom the group consisting of acetic acid, hydrochloric acid, sulfuricacid, nitric acid, carbonic acid, lactic acid, citric acid, phosphoricacid, oxalic acid, and mixtures thereof.
 19. The method of claim 1,wherein the second treatment composition comprises: (i) polyethyleneimine, polyglucosamine, and mixtures thereof; and/or (ii)3-aminopropyltriethoxy silane.
 20. The method of claim 1, wherein thefirst reaction of (2) is a condensation reaction effected by contactingthe membrane of (1) with a basic solution.
 21. The method of claim 20,wherein the basic solution comprises a base selected from ammoniumhydroxide, sodium hydroxide, potassium hydroxide, lithium hydroxide,calcium hydroxide, and mixtures thereof.
 22. The method of claim 20,wherein the second reaction of (4) is effected by contacting themembrane of (3) with an acidic solution.
 23. The method of claim 22,wherein the acidic solution comprises an acid selected from acetic acid,hydrochloric acid, sulfuric acid, nitric acid, carbonic acid, lacticacid, citric acid, phosphoric acid, oxalic acid, and mixtures thereof.24. The method of claim 20, wherein one or both of the first reaction of(2) and the second reaction of (4) occur(s) at ambient temperature. 25.The method of claim 22, wherein the microporous membrane is a componentof a filter device.
 26. The method of claim 1, wherein one or both ofthe first reaction of (2) and the second reaction of (4) is/are effectedby exposing the membrane to elevated temperature.
 27. The method ofclaim 26, wherein the temperature ranges from 50° C. to 145° C.
 28. Atreated microporous membrane prepared by the method of claim
 1. 29. Atreated microporous membrane prepared by the method of claim
 26. 30. Atreated microporous membrane prepared by the method of claim 20, whereinthe treated membrane is a component of a separation device.
 31. Thetreated microporous membrane of claim 29, wherein the treated membraneis in the form of a sheet.